metabolic response to exercise 2

Lactate threshold

• as exercise intensity increases during an incremental exercise test blood levels of lactate rise exponentially

  • appress at 50-60% VO2 max in untrained individuals

  • higher work rates in trained individuals 65-80% VO2 max

• as acidosis changes

  • shift in ATP

  • stimulate glycolytic pathway

  • AMP stimulates glycolysis

• incremental exercise

  • measure in blood

• switch will move LDL in that direction

• increase free fatty avid metabolism

  • protein coupled receptors

OBLA

• onset of blood lactate accumulation

• Differs from lactate threshold as it is not a blood lactate inflection point but instead the exercise intensity at which a specific blood lactate concentration is reached

lactate threshold vs anaerobic threshold

• anaerobic threshold is sudden rise in blood lactate concentration whereas LT is the incremental rise in lactate threshold is a measurable physiological point where lactate production exceeds removal

• 2 intensities

  • mitigate or alter start of LT

    • want to control intensities until this point

  • within OBLA

    • anaerobic threshold

  • CO2 potent vasodilator of coronary and cerebral arteries

    • CO2 drops and blood flow may begin to drop

    • delivery is more than flow

      • flow X O2 []

high intensity exercise training on lactate/H transport capacity

• single leg exercise 3x/week for 1st 5 weeks then 5x/week for following 3 weeks

  • 8 weeks of single leg training 

• resistance standardized based on Newtons 

  • plasma blood lactate increased 

    • increase peak power, mean power, endurance 

      • systems were more efficient at producing lactate 

        • better at using glycolytic system 

        • increase in MCTs [] increase in lactate 

• results

  • improved lactate and H transport 

    • MCT and HAD

  • improved anaerobic and aerobic performance 

  • improved isometric force 

  • no change in bicarbonate 

    • increase carbonic anhydrase 

      • more efficient in moving CO2

practical uses of lactate threshold

• anaerobic threshold 

  • classic term used to describe the intensity / work load at which anaerobic metabolism became prevalent

    • was used synonymous with LT

• lactate threshold

  • point at which blood lactate levels being to rise exponentially during exercise (50-60% VO2 max)

• maximal lactate at steady state

  • maximal lactate achieved at steady state workload

• critical power

  • point at which workload can me maintained at a steady state 

• metabolic response is different for each individual leading to different genetic expression

  • exercise at different relative percentage of output

    • different absolute workloads

    • differences in substrate utilization

      • glucose, lipid, lactate, ketone

        • not a macromolecule

cross-over concept

• As intensity increases progressive increase in CHO metabolism and decrease in Lipid metabolism

•   there is an intensity at which the energy derived from CHO exceeds that of fat

  • This point is the cross-over point

• Recruitment of fast fibres and increasing blood levels of epinephrine causes this shift from fat to carbohydrate

  • The abundance of glycolytic enzymes in type 2 fibres but few mitochondrial and lipolytic enzymes

    • Better equipped to metabolize CHO than fats

      • Increased recruitment results in greater CHO metabolism and less fat metabolism

• Epinephrine increases a progressive rise in blood levels of epinephrine

  • High level of epinephrine increases phosphorylase activity causing an increase in muscle glycogen breakdown

    • Increased rate of glycolysis and lactate production

      • Inhibits fat metabolism by reducing availability of fat as a substrate

        • This makes CHO the primary fuel 

        • longer production increases fatty acid beta oxidization 

exercise duration and fuel selection

• Prolonged moderate exercise (greater than 30 mins) the R decreases over time

  • Indicates gradual shift form CHO metabolism toward and increasing reliance on it as substrate

rates of glycogen breakdown for various exercise intensities

• Heavier the exercise the faster glycogen is broken down

  • Initiated by second messengers which activate protein kinase in the muscle cell

• Plasma epinephrine

  • Stimulator of cAMP formation when bound to beta-adrenergic receptors was believed to be primarily responsible for glycogenolysis

exercise intensity and substrate utilization

• restore glycogen stores 

  • absolute fat percentage 

interaction between bioenergetics and fuel source

• glycogen depletion reduces rate of glycolysis 

  • lowers pyruvate 

  • reliant blood glucose and plasma FFA

• lower levels of pyruvate reduced Krebs intermediates and slow Krebs acitvity 

  • decrease in glycogen increase in glycolysis increase n plasma FFA 

    • maintain glycolytic pathways 

    • still need carbohydrates 

• Contribution of plasma FFA and muscle triglycerides to exercise metabolism during prolonged exercise shows that at beginning of exercise contribution of plasma FFA and muscle triglycerides is equal

  • As duration of exercise increases there is progressive rise in role of plasma FFA as a fuel source

Carbohydrate storage sites

• protein contributes less than 2% of fuel used during exercise of less than 1hr in duration 

  • may increase to 5-10% in longer duration exercise

• IMTGs begin to alter ROS

  • both exercise and nutrition

    • double whammy

• changes genetic expression due to changes in mitochondrial biogenesis 

  • M4 expression of GLUT4 receptors

  • mitochondrial biogenesis

    • changes cytochrome oxidase in ETC

carbohydrate restricted training

• limitation of these steps of fatigue levels 

• fasted training - liver glycogen lowered 

  • enhances genes linked to substrate utilization and mitochondrial function 

• low glycogen (2x/day training)

  • increase citrate synthase and exercise capacity 

    • 1st session burns most of glycogen 

      • don’t restore most stores 

        • citrate synthase is rate limiter of Krebs 

          • can increase glycogen capacity 

• post exercise CHO restriction

• Sleep low - train low

  • improves gene expression (PGC-1a etc)

  • greater fat oxidation - similar gene expression

  • improved cycling efficiently and TT performance

  • exercise before sleep and then exercise again without fuelling

VO2 in men and women

• women have lower absolute VO2max than men 

  • less of a difference when comparing relative VO2max

• size and body composition impact VO2

  • more muscles we use the higher the VO2 

• when we control for body size the difference between men and women lessens 

exercise intensity in makes and females

• menstrual cycle is variable

  • shifts energy consumption and utilization

• oral contraceptive use

  • different types may confound

  • estrogen blocks and alters epinephrine pathways

• important to consider other physiologically relevant factors

  • body fat percentage

  • mass

  • height

• pathological differences 

  • lean muscle mass matching to compare 

    • fat does not use as much oxygen 

    • structural components are controlled 

fat oxidation in women and men

• better in women

• increased type 1 fibre % 

  • increased mitochondria, myoglobin and capillary density are designed for aerobic metabolism

    • preferentially use fatty acids

• increases IMCL availability

  • store more IMCL droplets near mitochondria in type 1 fibres

  • readily accessible fuel source

• increased adipose FFA production

  • greater lipolysis leasing ot more circulating FFAs

    • more substrate available for oxidation by muscle

• increased FFA oxidative protein expression

  • high levels of fat transport and oxidation proteins

    • improves ability to transport FFAs into mitochondria and oxidize them

• women have machinery due to increased fat stores

  • change in estocyles - change in estrogen 

  • lowers RER

impact of exercise intensity on bioenergetics and metabolism

• changes in GLUT4 proteins 

• RER shift 

• increase or change in TFPalpha 

  • provides or improves lipolysis

cori cycle transporters

1. lactate transporter

   1. muscle cells ↔ blood ↔ liver

   2. MCTs uptake lactate into the liver

      1. follows concentration gradient

2. Glucose transort

   1. liver ↔ blood ↔ muscle

3. pyruvate transport

   1. mitochondrial pyruvate carrier

      1. imports pyruvate into mitochondria for gluconeogensis or TCA cycle activity

McArdle’s syndrome

• Genetic disease cannot synthesize phosphorylase enzyme

• Prevents breakdown of muscle glycogen as a fuel source during exercise

  • Prevents muscle from producing lactate

    • More fat used at submaximal exercise ompared to control

      • Not able to oxidize more fat

      • Carbohydrate availability limits fat oxidization even during steady-state exercise 

is low intensity exercise best for burning fat

• Overal energy expenditure is also very low at low exercise intensities

  • Only a small amount of fat is oxidized

• Fat oxidizartion increases up utni 60% VO2 max before decreasing this means that

  • The highest rate of fat oxidation seems to appear right before the LT